$26.25
Explanation:
We are told that Marco needs to buy some cat food. At the nearest store, 3 bags of cat food cost $15.75.
First of all we will find cost of 1 bag of cat food by dividing 15.75 by 3.
Now we will find the amount that Marco has spend for 5 bags of cat food by multiplying 5.25 by 5.
Therefore, Marco has spend $26.25 for purchasing 5 bags of cat food.